Process of concentrating nitric acid.



OsKAR Bonrnns, subjects of, the

lINl an sTATEs RICHARD ll'OLFFENSTEIN EAlENT OFFICE.

AND OSKAR BOETERS, o1 BERLIN, GER-MANY.

PROCEsS OF CONCENTRATINGNITRIC ACID.

To all whom it may concern:

Be .it known that we, RICHARD 'OLFFENSTEIN and German Emperor, residing at Berlin, Germany, have invented a certain new and useful Process of Concentrating Nitric Acid, of

whichthe following a sp'ecification. 1

"At present the concentration of. dilute. nitric acid is generally effected by means of concentrated sulfuric a'cidl Th is method has various drawbacks. In he;

first place it requires the erection of a sulfuric acid lacfor the regenerationof'the sulfuric acid used for concentration, because the latter volatilines after having reached certain degrees of-concentration. Moreover, the concentrated sulfuri'c'acid has a decomposing effect on the nitric acid. Consequently the process is irrational and complicated, This. evil is well-known; at

tempts have therefore beeninade to render the concentration of nitric acid possible by other methods, and the patentliterature mentions various processes which have this object According to oneof these processes cal- .ciunichlorid and magnesium chlorid are to be used for the concentration of nitric acid;- The use of these salts,

howevergentails the evil, that the strong nitricacid sets freealso hydrochloric acid from the salts, whereby i the nitricacid is rendered impure; I For this reason the inventors of such processes have not used the salts in a solid state, but only solutions of the same, whereby they deprived themselves at the start of a large portion of the desired effect.

According to another process anhydrous sodium-sul-- fate or calcium-sulfate is used, over which substances the nitric acid heated above the boiling point, conducted. The method of actionof these salts, however,

is very limited,.for Glaubers salt yields up its water of i rystallization at temperatures. over 33 0., and gypsum loses-its Water at 110 C'., that is to say, zit-temperatures so low that a rational abstraction of water from dilute nitric acid heated above the boiling'point cannot take place. In practice none" of these processes seems to have beenadoptedtoa-ny considerable extent, in con;

sequence of which the concentration ofnitric acid by v I 1 I means'ot concentrated sulfuric acid is still mosttrequently used. We have ascertained, that the concentration of nitric acid may be effected far more advantageously by means of nitrates capable of entering into chemical combina tion with water, such'as calcium. nitrate and magne- I 'n comparison with that generally used is based on the fact, that it saves thebuilding and working of a sulfuric acid factory, and that the productionof nitrous gases, which is liable to take place in the ordinary process through the action of conc ntrated sulfuric acid, is avoided.

The present process is carried out simply bydehydrating for instance the calcium-nitrate, at 150-200 Specification of Letters Patent. Application filed Deccniber 17, 190 6.

and after cooling to about-50 C., pouring over it the nitric acid to be concentrated. In consequence of this treatment the nitric acid is deprived of water, when the heating is renewed, and distils over inn concentrated condition, whilethe calcium nitrate rev-absorbs water.' It now the temperature is again raised to about 150 to 200?' C the calcium nitrate, rcmainedbehindin.the re: tort, yields up Water (4 molecules) which it had absorbed, becomes anhydrous and may be used again for the extraction of water. r

A specialadvantage of the application of calcium nitrate is the fact, that this salt swells up andbccomcs highly porous, thus presenting tion a large surface. g I

It is adv-arnagwus to carry out the process by making. use .of the principle of counter currents, that is to say the untreated and thcreforeweakest nitric acid is first brought together on; the nitrate which has absorbed a considerable quantity of water, while the partly treated and therefore stronger nitric acid comes in'contact with nitrate whichcontains less water and is therefore capable ofabstracting water from-the partly concentrated acid.

As rbgards the quantity of materials used,-we have found, for example, that for concentrating ($3 per cent nitric acid, from '1}; to kilograms oi'calcium nitrate should be used for every kilogram of nitric acid.

- What we claim is: 1 i

1. The imprbveme nt in theart of concentrating nitric acid. which consists in treating it with an anhydrous p *rnte capable of combining chemically with water. substantlaily described. v p I "2. The process for coneen sting dilute nitric acid. which consists in heating a hydrated nitrate so as to 'drive out the water. then allowing it to cool. pouring over it the nitric acid to be concentrated; amltlien distilling of!- and recovering" the nitric acid; substantially as described.

The herein described process for concentrating diluttnitric acid. which consists in dehydrating hydrated calclum nitrate by heat. allowingjt to cool. addingthe nitric acid to be ctmccntrated. and heating the mixture. so as to dislil (It the nitric acid. i l. The herein described process for concentrating dilute nitric acid. which consists in dclrvdratingh hydrated ni-' li'al'c by h ll allowing it to cool. adding the nitric acid H) be con cntraled. beating the mixture so as to disti l on ;1e the nitric acid. collecting the same and using the residue i ll'n '.rcpcutedly in the sumo manner.

.7. The herein described process for concentrating dilute nltricucid. which consists in dehydrating .a hydrated nitrate by heat and in rum/n. addingthe nitric acid to bc' cont-mltrrrfll. heating the mixture so as to distil off the nitric acid. collecting the same'and using the residue of nitrate rcy'lealcdly in the same manner.

In testimony whereofwe have set our hands hereunto in the n-escnkre of two subscribing witnesses.

Witnesses Enron Tnr'rxua,

ARTHUR Mansosn.

to the nitric acid solulot 

